Efficiency Enhancement of Class-J Power Amplifiers by Injecting Second Harmonic Into the Gate and Drain Node Simultaneously

In this letter, a design methodology is proposed to improve the efficiency of class-J power amplifiers (PAs). By injecting the second harmonic into the gate and drain node simultaneously, both the intrinsic drain voltage and current waveforms of the ideal class-J PA are reshaped, leading to a smaller phase shift, and consequently, higher efficiency has been obtained. In addition, the detailed design guideline of the proposed structure is provided. Based on it, a proof-of-concept circuit with a commercial GaN transistor is designed. The measured result shows the power-added efficiency (PAE) of 78.6% and gain of 14.3 dB at 1.69 GHz. To the best of our knowledge, this is the highest PAE of class-J PAs at L-band.